Sam Fawcett, Manager of the Centre for Coastal Technologies, discusses the role modelling plays in mCDR (marine carbon dioxide removal) development and how this important tool can help us move forward with mCDR research and methods.
To slow down the effects of climate change and create a sustainable future, scientists are researching and implementing methods to both reduce carbon emissions and remove existing carbon dioxide to drastically reduce levels in the atmosphere. mCDR stands for marine carbon dioxide removal; it is a technique used to enhance the ocean’s natural ability to store carbon dioxide. The methods range from natural solutions to engineered carbon removal.
The ocean naturally absorbs about 25% of annual CO₂ emissions and is the planet’s largest store of CO₂, making it a logical target for enhanced carbon removal. To ensure we fully understand the efficacy and environmental impacts of different types of mCDR, scientists use modelling to investigate the likely effect on the marine environment of several methods of mCDR and evaluate their success at removing carbon dioxide.
What is mCDR modelling?
mCDR modelling provides a simulation environment for testing different approaches to predict what would likely happen in the real world. Currently, modelling is one of the best options for planning pilot studies and assessing upscaling while minimising the risk of expensive failure. Given the complexity of the marine environment, with factors such as variation in mixing at small and large scales and complex biogeochemistry to consider, it is unlikely that any mCDR exercise could be characterised by observations alone, meaning modelling is an essential step in the development process.
Initially, mCDR modelling using high-resolution, local-scale setups can determine whether the mCDR plans are potentially viable. Steps can then be taken to trial an mCDR method in real-world conditions, with observations used to confirm or improve model skill. If viability and ecological safety are indicated, the goal is to then scale up the method to remove large quantities of carbon dioxide, initially testing this with larger-scale models.
Marine system modelling is a well-established systematic approach to creating simplified representations of complex real-world systems using mathematical equations, computational algorithms and theoretical frameworks. Several extent model systems provide a suitable basis for modelling mCDR, as they include detailed, sometimes high-resolution hydrodynamics, state-of-the-art descriptions of carbonate chemistry and descriptions of relevant biochemical processes.
Suitably adapted, these models simulate the impact of mCDR technology on ocean water and, by extension, what impact this could have on the marine environment. Further to this, they can simulate the rate at which the oceans’ CO₂ will re-equilibrate with the atmosphere and the long-term fate of sequestered CO₂ – the ultimate goal of mCDR.
Dissolved Inorganic Carbon Chart, Yaru Li
There are two fundamental questions that mCDR modelling looks to address:
- What impact might the mCDR approach have on the marine environment? i.e. in principle, is the method safe for the marine environment?
- To what extent will CO₂ be drawn down from the atmosphere, and for how long is it likely to remain locked in the oceans as a result? i.e. is the method viable for removing CO₂ from the atmosphere in the long term?
The ideal outcome to the first question is that the treated water equilibrates readily with the atmosphere and that the environmental impacts are tolerable. This information can then be used in a company’s business plan to attract further funding for development.
The environmental impact that is being monitored includes:
- Ocean chemistry changes including pH, dissolved oxygen, carbonate saturation
- Ecosystem impacts
- Biogeochemical impacts – nitrogen, phosphorus and other nutrients
pH Chart, Yaru Li
To the second question, we would hope to see that the method is both effective for long term storage and has a low environmental impact. It is also important to consider factors such as the carbon emissions the technology emits and whether the method for removal can be scaled up.
The reason we ask the second question is that the scale required to make a meaningful climate impact is enormous, which is why we need the modelling stage to understand feasibility.
The overall desired outcome from modelling trials is a combination of scientific understanding and practical field trial guidance.
mCDR interventions could have significant detrimental ecological consequences if conducted irresponsibly. Models help identify potential negative impacts and target environmental monitoring efforts before conducting field trials, to protect marine ecosystems from unintended harm. Working with organisations such as PML Applications ensures these factors are being thoroughly considered and tested at every stage of an mCDR trial.
The Centre for Coastal Technologies (CCT) team at PML Applications has conducted mCDR modelling, ranging from small mesocosm scale through to large coastal domains. Our team also works on decision-making support tools to provide organisations with a usable tool that they can manipulate to answer deployment questions.
Find out more about our mCDR services here
mCDR modelling is one stage in mCDR development. Before conducting a simulation using modelling, a trial may begin with laboratory and analytical services that inform decisions about dosing, dilution parameters and operational limits of the mCDR technology, using controlled chemical analysis.
After this has been conducted, the next service in our phased and gated approach to mCDR development is modelling. Using hydrodynamic and biogeochemical modelling, the effectiveness of mCDR methods can be quantified using a three-phase system:
- Phase 1: Custom model development using FVCOM (Finite Volume Community Ocean Model) coupled with ERSEM ecosystem modelling.
- Phase 2: Scenario analysis to quantify CO₂ uptake, export dynamics and plume dispersion.
- Phase 3: Performance assessment across operational scenarios and uncertainty analysis.
The models are designed to address key uncertainties, including CO₂-depleted water retention, air-sea gas exchange rates, and complex coastal dynamics.
It is important to understand and monitor the behaviour of CO₂-depleted water when reintroducing it into the marine environment using the following parameters:
- CO₂ Uptake: The rate at which the CO₂-depleted water absorbs CO₂ to return to its natural composition.
- Plume Dispersion: The rate at which the mass of CO₂-depleted water mixes with the surrounding water to reach the same composition.
- Export Dynamics: The transference of CO₂-depleted water from the surface to the deep ocean.
If this phase is successful, it is followed by mesocosm ecotoxicology studies to conduct a thorough environmental impact assessment. These studies are either short-term (72 hours) or long-term (30 days). There is a particular focus on how the proposed mCDR method will impact local organisms and sensitive habitats.
In some cases, eDNA is used to detect the presence of species and monitor any changes.
Next, the study can progress to a field trial where samples are taken using tools such as automated systems and sensor deployment on land. At sea, techniques include mobile vessel-based surveys, buoy-based monitoring, and environmental monitoring. A baseline is taken of plankton communities, intertidal macroalgae and invertebrates to monitor any changes.
The final stage, once the above trials have had positive results, is documenting and reporting for carbon credit verification.
Modelling is an essential step in this process as it provides a method for testing that is hypothetical and therefore does not cause physical harm to the environment. By testing and adjusting based on the results of modelling, once testing reaches field trials, there is better control due to the previous predictions.
Our modelling expertise is underpinned by over 20 years of experience in modelling CO₂ in marine systems, initially in the context of geological carbon storage EIA (Environmental Impact Assessment) and ocean acidification research. CCT combines our modelling experience for mCDR with practical experience of conducting mCDR field trials, providing pragmatic and realistic suggestions at each stage of development.
